SEX-SPECIFIC DNA METHYLATION SIGNATURES IN PANIC DISORDER

Background Panic disorder (PD) is characterized by sudden episodes of acute anxiety occurring without any apparent reason. PD is the most disabling anxiety disorder and it affects twice as many women as men. The heritability of PD is estimated to be up to 48% and epidemiological studies show that both cumulative and specific life events are risk factors for the development of PD. Therefore, the investigation of genetic factors and gene-environment interaction is of high importance for understanding the pathophysiology of PD. As such, examining epigenetic differences in PD patients is of great interest given that environmental factors, in combination with genetic variation, can influence DNA methylation. Methods We conducted an Epigenome-Wide Association Study (EWAS) comparing non-medicated PD patients (49 females, 40 males) with healthy controls (48 females, 28 males). Replication was sought in an independent sample (131 cases, 190 controls) and further confirmed with a meta-analysis across both samples (220 cases, 266 controls). DNA methylation levels were assessed in whole blood using the Infinium HumanMethylation450 BeadChip. Failed probes were excluded based on a detection p-value larger than 0.01 in u003e50% of the samples. X chromosome, Y chromosome and non-specific binding probes were removed. The data were normalized with functional normalization in Minfi and batch-corrected using ComBat. Regression analyses accounting for cellular heterogeneity, sex and age were performed to test for associations between PD status and DNA methylation. To further assess functionality of the significant CpG, gene expression profiles (Illumina HumanHT-12 v3.0 array) in peripheral blood before and after exposure to the glucocorticoid receptor agonist dexamethasone were tested for association with DNA methylation in another independent female sample (N=71). Results No genome-wide associations were observed in PD patients compared to controls in the whole sample. Interestingly when stratified by sex, only the comparison of female PD patients with controls yielded one genome-wide association surviving FDR of 5% (P= 1.094 x 10-7 , P-adj=0.046). Specifically, cg07308824, located in the promoter of the HECA gene, was hypermethylated in female PD patients (N=49) compared to controls (N=48). The same CpG was also hypermethylated in female PD patients in the replication sample (P=0.035) and the genome-wide significant association was confirmed in the meta-analysis (P-adj=0.007). Methylation at this CpG site was associated with mRNA expression of HECA both at baseline (P= 0.046) and after induction by dexamethasone (P= 0.029). Pathway analyses using Web Gestalt investigating the top 50 associated CpG sites showed enrichment in female-specific pathways, e.g. female infertility pathways. Discussion Our study is the first to examine epigenome wide differences in peripheral blood for PD patients. Interestingly, our results point to possible sex-specific and functional methylation changes in PD. Further studies are needed to examine a possible contribution of the HECA gene methylation to female specific factors in PD.